Crockpot Choice Advice

I am getting so frustrated with crockpot/slow cookers. My old one died, it was old when I got iit years ago. I now have four new ones, a four quart, five quart and two six quarts. None are fancy, dial, and one push button. Here is the problem. I know that newer models cook hotter than the old ones but I find things scorch and boil even on the low settings. The five quart is way too hot, the four quart just scorched the bottom of a cake at the 4 hour mark on a five hour recipe. I use the six quarts for stews, roasts, chilis, etc. and for when we have big gettogethers and it is ok.
My question for y'all is whether a more expensive model is worth the money. I know it probably sounds silly but I use a crockpot because it is easy and foolproof, don't want to burn another batch of carmelized onions, cake, or other "easy" food.